1. Field of the Invention
The present invention relates to a diaphragm device for changing a shutter aperture diameter in a step-wise manner.
2. Description of the Related Art
A known diaphragm device is described in Japanese Patent Laid-open No. 79541/1993 by the present assignee. This known diaphragm device will be explained with reference to FIG. 8.
In FIG. 8, a rotor 10 formed by a permanent magnet, a rotor actuated lever 11, a diaphragm actuating member 12 and a small-diaphragm plate 73 are pivotably supported on a main plate (not-shown) through a rotor shaft 10a, a shaft 12a and a shaft 4. The small-diaphragm plate 73 has a sufficient overall size to cover the shutter aperture 2 and has a small-diameter diaphragm aperture 73a. The small-diaphragm is pivotably supported by the shaft 4 to move between a first position A fully covering the shutter aperture 2 and a second position B fully retracted from the aperture 2. Also, the small-diaphragm plate 73 is urged in a clockwise direction in the drawing by a spring 73c and abutted against and rested on a positioning pin 5.
The diaphragm actuating member 12 is latched and biased in a counterclockwise direction in the drawing by a spring 13, and is abutted against an engagement pin 14.
When a coil L is energized to excite the stator 9, the rotor 10 rotates in a counterclockwise direction and the rotor actuated lever 11 fixed on the rotor shaft 10a also rotates in a counterclockwise direction. This rotation causes the diaphragm actuating member 12 to rotate in a clockwise direction through a rotor actuated lever pin 11a. Through a protrusion 12b of the diaphragm actuating member 12, the small-diaphragm plate 73 is rotated counterclockwise about the shaft 4 from the second position B to the first position A where it goes into abutment against a positioning pin 15. Consequently, the shutter aperture 2 is restricted by a diaphragm aperture 73a. At this time, a pin 73b fixed on the small-diaphragm plate 73 moves a movable iron piece 18 along an attraction surface of an iron core 17a. At a time that the small-diaphragm plate 73 reaches the first position A, an electromagnet 17b is excited to attract and hold the movable iron piece 18, maintaining the small-diameter diaphragm aperture 73a. 
In this related-art diaphragm device, the small-diaphragm plate 73 is structured by one plate and has a sufficient size to fully cover the shutter aperture 2. Because the small-diaphragm plate 73 has a size large enough to cover the shutter aperture 2 when in the first position A, it must be moved by a large amount to the second position B to be fully retracted from the shutter aperture 2. This requires the small-diaphragm plate 73 to be dimensioned to provide a large space for retraction, resulting in an increased size in the vicinity of the shutter aperture 2.
In order to solve the above problem, a small-diaphragm plate is provided with a diaphragm aperture smaller in diameter than a shutter aperture and an auxiliary plate so that when the small-diaphragm plate is selected, the small-diaphragm plate and the auxiliary plate cooperate to cover the shutter aperture. Since the small-diaphragm plate is provided in a divided manner to cooperate with the auxiliary plate, the small-diaphragm plate can be made smaller in area than in the conventional device, making it possible to reduce the size of the diaphragm device.
A diaphragm device according to one aspect of the present invention comprises a small-diaphragm plate having a diaphragm aperture smaller in diameter than a shutter aperture and being movable between a first position at which the diaphragm aperture is positioned in the shutter aperture and a second position at which the diaphragm aperture is retracted from the shutter aperture, an auxiliary plate cooperating with the small-diaphragm plate to cover the shutter aperture, and a diaphragm actuating member for actuating the small-diaphragm plate or the auxiliary plate, wherein actuation of the diaphragm actuating member causes the small-diaphragm plate to be moved to the first position and the auxiliary plate to be moved to a first position covering the shutter aperture, and actuation of the diaphragm actuating member in the other direction causes the small-diaphragm plate to be moved to a the second position and the auxiliary plate to be moved to a second position retracted from the shutter aperture. Because the shutter aperture is covered by cooperation of the small-diaphragm plate and the auxiliary plate, the small-diaphragm plate can be made smaller than in the related device, making possible to reduce the dimensions in the periphery of a shutter.
The auxiliary plate may be positioned on a side opposite to or the same side of the shutter aperture as the small-diaphragm plate when the small-diaphragm plate is positioned in the second position. This structure improves the freedom in arrangement of parts around the periphery of the shutter.
Actuation of the diaphragm actuating member in one direction may be conveyed through the small-diaphragm plate to the auxiliary plate to move both in unison or may be conveyed through the auxiliary plate to the small-diaphragm plate to move both in unison. This structure improves the shape and freedom of the arrangement of parts. Also, the diaphragm actuating member if driven by a motor will achieve automation of the diaphragm device.